Method of vulcanizing rubber and resulting products



Patented Nov. 5,1929

HENRY B. MORSE,'OF DANV'ERS, MASSACHUSETTS, ASSIGNOR, IBY MESNE ASSIGNMENTS,

TO ALBERT C. BUB-RAGE, .13., OF IPSWICH, MASSACHUSETTS METHOD OF VULCANIZING RUBBER AND RESULTING PRODUCTS No Drawing.

This invention relates to the art of treating rubber or rubber compounds, and has for an "object the provision of an improved procedure. for the vulcanization of the same in the presence of an accelerator and of compounds or compositions with which to effect the purpose of the invention. In the art of rubber maniifacture, it has long been known that the vulcanizing process may be accelerated by the addition of various compounds in relatively small amounts. The compounds which have been found to thus accelerate vulcanization, known as accelerators, have been constantly added to by re- 5 search and now include numerous types of substances,-both inorganic and organic. these substances, the organic compounds are preeminently the more satisfactory and PI'G".

sent a wide range of accelerating activity. Those selected for practical use, however, ar generally restricted to compounds which may be mixed'with the rubber or rubber compound without inducing appreciable vulcanizing effeet at atmospheric temperature or during milling operations, but which actively accel .erate the reaction in the customary vulcanizin'g treatment. Other accelerator compounds, frequently termed (ultra-accelerat0rs or semiultra accelerators, initiate the vulcanizing reaction sometimes prematurely, either in the cold only or during the mixing operation, resulting in scorching which hinders or entirely prohibits the further use of the rubber or rubber compound. Conse- 5 quently, such compounds ordinarily have not been used in the manufacture of rubber products, even though they would greatly reduce the time required for vulcanization and may be otherwise suitable for use in rubber com- 40 positions.

By the present invention it is found that the accelerating action of accelerator compounds generally in rubber compositions, may be inhibited (at ordinary and slightly elevated teinperatures and during the mixsometimes referred to as semiultra accel- Application flled ibecember a, .1928, Serial No. 323,556.

ing and milling operations) or retarded by the addition of organic compounds of a certain type hereinafter defined, and that thereafter the vulcanizing reaction,efiectively accelerated by the accelerator,-may be caused to proceed at will by subjecting the I rubber composition to be vulcanized to vulcanizing conditions.

In other words, the critical temperature of the acceleratorywith respect to its initiating prematurely the vulcanizing reaction in the rubber, is apparently raised to a point above the temperatures of milling or compounding and within the range of the vulcanizing treatment.

The coinpounds manifesting. such inhibiting action upon premature initiation of vulcanization b accelerators (and more especially the ultra accelerators and those I erators among which may be mentioned the thiazoles, represented by mercaptobenzo thiazole, certain disulphides such as tetra methyl thiuram disulphide, certain monosulphides such as tetra methyl thiuram monosulphide, etc., and their derivatives) are found to typically include the nitroso-amines which may be represented by the empirical formula: I

in which R and B. may represent aryl radicals and may be alike or unlike. so

In a representative example of the inven- In a preliminary scorching test, for example, in which the compounds were subjected to especially high temperatures during the mixing and milling operations until scorching was effected, a rubber composition containing 100 parts rubber (smoked sheet) 3 parts sulphur 5 parts ZnO I part mercapto benzo thiazole to which .43 part dibeta naphthyl nitrosoamine was added, was thoroughly milled and mixed on the mixing rolls. The mix was then removed and again milled onrolls, purposely heated by steam so as to maintain a temperature in the stock of approximately 95 to 100 G.,for 110 minutes before "scorching occurred. I

A corresponding stock without the addi-- tion of dibeta naphthyl nitroso-amine, upon being milled and mixed, and again milled inder like conditions of temperature, scorched in 65 minutes.

A similar test carried out upon a rubber compound of the formula:

100 parts rubber (smoked sheet) 3 parts sulphur e 5 partsZnO a .15 part1;1 tetra methyl ,thiuram disulide .75 part dibeta naphthyl nitrosoamine produced scorching in about 7 2 minutes. Un-

der like conditions the same compound, with out the dibeta naphthyl nitroso-amine, was

I scorched in twenty minutes.

A third compound, having the formula:

- 100 parts rubber (smoked sheet) 3 parts sulphur 5 parts ZnO .15 part tetra methyl thiuram monosulphide A .75 part dibeta naphthyl nitrosoamine I hibiting eflect of the inhibiting compound upon the vulcanization reaction and the accelerating influence. of the ultra accelerator at "temperatures of about 100 C. or less, as contrasted with vulcanizing temperatures which as ordinarily employed are above 120 C.

In a typical application of the invention to the usual vulcanizing procedure, rubber compounds were prepared as follows:

100 parts rubber 4.0.5 parts carbon black 5.0 parts ZnO 3.0 parts sulphur 5.0 parts mineralrubber 3.0 parts stearic acid .8 part mercapto benzo thiazole Same as Formula I with additionof 1.0

part diphenyl nitroso-amine.

III

part diphenyl nitroso-amine.

Same as Formula I with addition of .50 part diphenyl nitroso-amine.

These were mixed by milling in the manner, care being taken, especially with the compound of Formula I, to prevent preliminary vulcanization or scorching. The mixed compounds were then laid in thin sheets in a vulcanizing mold and vulcanized at 20 pounds steam pressure. Samples of each compound were vulcanized, for periods of 30, 45 and 60 minutes, respectively. One portion of each sample was then subjected to a tensile strength test, the results being given in the following tables Table I Cure at twenty pounds steam pressure usual 30 Minutes gin l {Final ns 0 e onga- 300% 500% lbs. tionin sq. 11. per cent II A 380 1140 2120 075- III A 583 1015 2930 080,

IV A 637 1820 e100 ass 7 45 Minutes L I i e1 11 us e 0 BB- 300% 500% lbaper tionin 3 sq. 11. per cent 1;. A 958 2420 4050 070 1r A -71 2 2000' 3420 080 III A 948 2440 4125 675 IV A 910 2500 4150 075 4 observed that rubber compounds prepared 60 Minutes an accelerator containing a thiazole nucleus, characterized by controlling the action of the g g gg accelerator with dibeta naphthyl nitrosm 300% 500% lbs. per tionin r 1 v 5. Method of vpllcanizing rubber or rubbei 4 compositions Wit a vu canizing agent'an I A 1105 4050 640 mercapto benzothiazole characterized by 0011- A 985 trolling the action of the accelerator with m A 1135 2880 4115 dibeta naphthyl nitroso-amine. IV A 1120 2930- 4280 s25 6. An accelerator composition comprising From the data thus obtained it is to be with an addition of the diphenyl nitrosoamine are free from the tendency toward preliminary vulcanization or scorching, and

,when vulcanized at pounds steam pressure and for the periods of time indicated, the vulcanized product exhibits a superior 'cure (both with respect to intermediate and finalelongation values) than the composition to which such addition has not been made.

"It is therefore shown that by means of this invention not only may extremely active accelerators, (which have been hitherto unavailable for use in the rubber industry on account of their very high activity) be safe- 1y employed in rubber compounds and mixed and milled without initiating premature vulcanization, but the vulcanized rubber product is initially better than rubber similarly compounded and vulcanized but without the addition of an inhibiting reagent.

Compounds typical of the substituted nitroso amines above defined, which have been found suitable for use in accordance with the invention, include carbazole nitroso amine which can be spoken of as nitroso N-carbazole,

'2. The'process of preparing vulcanized .rubber which comprises treating rubber in the presence of'a vulcanizing agent and an an organic accelerator. and dibeta naphthyl nitroso-amine.

7. An accelerator composition comprising a sulphur-containing organic accelerator and dibeta naphthyl nitroso-amine.

8. An accelerator composition comprising an accelerator containinga thiazole nucleus and dibeta na thyl nitroso-amine.

9. An acce erator composition comprising mercapto benzo thiazole and Signed by me at Boston, Massachusetts, this 1st day of December, 1928. l v

- HENRY B. MORSE.

organicaccelerator, and controlling the acv tion of the accelerator with dibeta naphthyl nitroso-amine. r

3. Method of vulcanizing rubber or rubber compositions with a vulcanizing agent and a sulphur-containing organic I accelerator, characterized by controlling the action of the accelerator with dibeta naphthyl nitrosoamine. a

4. Method of vulcanizing rubber or rubber compositions with a vulcaniz'ing agent and dibeta naphthyl nitroso-amine. 

